We haven’t demonstrated the ability to go back because we don’t have that ability. NASA said once that if we wanted to we’d have to start from scratch and it would take something like 25 years. To which many, myself included, asked “wait, why did it only take like 8 years in the 60? And why not just use the plans from the one that worked and make one of them?” On the surface it sounds suspicious but probably the answer is “well, with current environmental rules we’d have to invent brand new materials that are eco-friendly and have the unique properties of the ones we can no longer legally use.” And like most eco-friendly substitutes, they’d be far inferior and probably more than a little dangerous.
I don't know where the 25 year number came from, but it depends heavily on how much money you're willing to spend and how fast you're willing to spend it.
It took longer than 8 years the first time, BTW. The Saturn V was in the planning phase in the late 1950's. It was easily 12 years from the beginning of the R&D to the first landing.
Why can't we build one again? Well, in part because the Saturn V is very old technology which was mostly hand-assembled by skilled craftsmen. We don't build stuff that way anymore, and we could build a much better rocket for much less money by using modern technology, computer-aided design, etc.
I said "less money," though, not "for free".
There was a time in my life that I believed what Walter Cronkite told me on the evening news. Our government, after killing Kennedy, needed distractions. One was Viet Nam. Another one was the Great Society and race-baiting. Still another one was the space program and it's "race to the moon". We were certainly distracted. Whether or not it was all faked is a legitimate question to ask of a government and news media that we have all learned the hard way is not worthy of our trust. I, for one no longer think we actually went to the moon much less landed on it.
“we don’t have that ability” NO. It’s because we don’t have the will.